1. Technical Field
The invention relates to heavy-duty vehicles, and in particular to frames and subframes for heavy-duty vehicles having improved energy absorption characteristics. More particularly, the present invention is directed to frames and subframes for heavy-duty vehicles which include a component that is disposed between the suspension hangers and the main members of the frame or subframe from which the hangers depend, or is incorporated into the hangers, and which absorbs energy that is created by a single-wheel impact or by a wheel becoming restrained in service, thereby reducing the possibility of damage to the hangers or the members of the frame or subframe caused by such an event.
2. Background Art
Heavy-duty vehicles that transport cargo, for example, tractor-tailers or semi-trailers, and straight trucks such as dump trucks, typically include leading or trailing arm suspension assemblies that connect the axles of the vehicle to the frame of the vehicle. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to a slider box, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle primary frames, movable subframes and non-movable subframes.
In the heavy-duty vehicle art, one or more axle/suspension systems usually are suspended from a single slider box. It is understood that a slider box outfitted with usually two axle/suspension systems typically is referred to as a slider or slider tandem, and for purposes of convenience and clarity, will hereinafter be referred to as a slider tandem. Of course, a slider box may also be outfitted with a single axle/suspension system, or three or more axle/suspension systems. By way of example, reference herein shall be made to a slider tandem having a pair of axle/suspension systems mounted thereon, with the understanding that such reference also applies to a slider outfitted with one, three or more axle/suspension systems The slider tandem in turn is mounted on the underside of the trailer primary frame, and is movable longitudinally there along to provide a means for variable load distribution and vehicular maneuverability.
More specifically, the amount of cargo that a trailer may carry is governed by local, state and/or national road and bridge laws, and is dependent on proper load distribution. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as limit the maximum load that can be supported by individual axles. A trailer having a slider tandem gains an advantage with respect to laws governing maximum axle loads. More particularly, proper placement of the slider tandem varies individual axle loads or distributes the trailer load so that it is within legal limits. Once properly positioned, the slider tandem is locked in place on the underside of the trailer by a retractable pin mechanism.
A slider box typically includes a pair of longitudinally extending elongated main members or rails that are parallel to one another The parallel spacing between the main members is maintained by cross members, which extend transversely between and are connected to the main members. The main members and the cross members of prior art slider boxes ate usually made of steel, which enables the cross members to be butted against and welded to the inboard surface of the main members. Other components that are part of or are related to the slider box, such as reinforcing members and suspension assembly hangers, typically are also made from steel and ate welded to the main members and/or the cross members It should be noted that, while the hangers are typically engineered as part of the axle/suspension system, they are often considered to be part of the slider box once they are connected to the main members of the slider box For the purpose of clarity, reference hereinafter shall be made to the hangers as part of the slider box. The slider box typically is movably attached to the vehicle primary frame by a retractable pin mechanism.
One consideration in the design of a slider box is durability. More particularly, heavy-duty vehicles, such as tractor-trailers, which contain more than one non-steerable axle are subject to lateral or side loads during vehicle operation. Lateral loads can act through the slider box in opposite directions, which in turn may create bending loads, the effect of which can be significant. Moreover, a slider box is often subjected to strong vertical and longitudinal loads. Thus, it is desirable to have a slider box with a durable design to control all of these loads.
Both the slider box and the axle/suspension system of a heavy-duty vehicle slider tandem must also be durable in order to withstand the force created by extreme events. Extreme events typically include single-wheel impacts caused by a wheel striking a bump in a road, a large pot-hole, a roadside guard rail, or a fueling station post, and the static hang-up of a wheel in service, which is a low-speed event wherein a tire is hung up or stopped temporarily during service until the vehicle pulls through the event. When a vehicle encounters an extreme event, vertical and horizontal crush forces are produced that potentially can cause significant damage to the slider box. More specifically, in a typical prior art slider tandem, when a vertical crush force is produced, a horizontal force in the rearward or aft direction also is produced, wherein the beam of a trailing beam axle/suspension system pulls toward the rear of the vehicle, in turn causing the rear portion of the hanger to which it is pivotally attached to impact or move vertically upward into the main member with significant force.
The vertical and horizontal crush forces may be of differing magnitudes at different points throughout the axle/suspension system, depending on the nature of the impact. For example, a static hang-up of a wheel in service is likely to produce a greater force than simply striking a bump in the road. A side force may also be produced if the impact is on a single wheel, which may cause the beam of the axle/suspension system to pull back and sideways, potentially causing the hanger to twist. These impacts could damage, or in an extreme case, cause the slider box main member and/or one or more of the attached cross members to fail, in either instance eventually requiring replacement, which is costly and time-consuming. Although the hanger typically is not damaged from such impacts, it usually also is replaced along with the main member. This design of a typical slider tandem causes many vehicles containing such slider tandems, including semi-trailers and tractor-trailers, to be out of service for extended periods of time after extreme events, such as single-wheel impacts, until the entire slider box can be replaced. This represents a significant problem in the trucking industry.
Another consideration in the design of a slider box is weight. More particularly, it is desirable to reduce the weight of a slider box as much as possible, while still maintaining performance characteristics and durability. Such a weight reduction decreases the amount of fuel that the heavy-duty vehicle consumes, leading to a reduction in fuel costs, and also enables more vehicle weight capacity to be devoted to the payload, thereby enabling a larger payload to be transported while the vehicle remains within the maximum weight limit that is set forth by load and bridge laws, thereby increasing the overall profitability of the vehicle.
To reduce the weight of the slider box, the use of structural materials that are lighter than steel, such as aluminum and aluminum alloys for the main members, cross members, and/or other components has often been explored in the prior art. However, certain characteristics of aluminum, such as high thermal conductivity and a low melting point, make the welding of aluminum components different, and potentially more difficult, than the welding of steel components In addition, aluminum components that are welded to one another or to a dissimilar metal, such as steel, may exhibit fatigue at the weld area, thereby potentially creating a weaker connection when compared to steel components that are welded together.
The potential for a weaker connection may become a concern at the interface between the main members and the hangers, and also at any interface between the cross members and the hangers. Since the axle/suspension system typically pivotally connects to the hangers, which are typically welded to the main members, the interface between the hangers and the main members is instrumental in reacting the loads or forces that act on the axle/suspension system, which may highly stress the rigid attachment of the hanger to the main member. Such stress may cause a welded connection that involves a material which is not readily welded, and therefore may be less than optimal, to undesirably fail, thereby reducing the durability of the slider box.
As a result, the limited ability of prior art heavy-duty vehicle frames and subframes to absorb the energy created by extreme events without significant damage, as well as the limited ability to provide an optimal connection between the hangers and the main members when lightweight materials are used, makes it desirable to develop heavy-duty vehicle frames and subframes that overcome these disadvantages. The present invention satisfies these needs.